The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Homogeneous charge compression ignition (HCCI) engines combust an air/fuel (NF) mixture within cylinders to produce drive torque. For example, in an HCCI combustion mode the A/F mixture may be automatically ignited when compressed by pistons (i.e. compression ignition). Alternatively, for example, in a spark ignition (SI) combustion mode the A/F mixture may be ignited by spark plugs in the cylinders after the pistons compress the A/F mixture. Moreover, there are transitions states between the combustion modes (e.g., transitioning from SI to HCCI).
The HCCI combustion mode may increase engine efficiency and/or fuel economy compared to the SI combustion mode. However, the HCCI combustion mode may be limited to a predetermined HCCI operating zone in order to reduce combustion noise and protect the engine from damage due to excessive pressure increases associated with HCCI. Therefore, pressure sensors may be implemented in one or more of the cylinders and may be used to monitor cylinder pressure, particularly during the HCCI combustion mode.
However, the HCCI combustion mode may also require precise control of A/F ratio, fuel injection timing, and other engine operating parameters to prevent decreased fuel efficiency and/or increased emissions. More specifically, lower peak temperatures during combustion (compared to SI combustion mode) may lead to incomplete burning of fuel and thus decreased fuel efficiency. Furthermore, nitrogen oxide (NOx) emissions may be higher during the HCCI combustion mode than in the SI combustion mode due to leaner A/F mixtures used in the HCCI combustion mode.